All
living organisms show a characteristic phenomenon of either moving their whole
body from one place to another place (locomotion or locomotory movement), or
only a part of the body while the whole body remains fixed to a place (movement
or non-locomotory movement). Various acts of the body like walking,
running, crawling, jumping, flying, swimming etc. are known as locomotory
movements. The locomotion helps the organism to shift its entire body
from one place to another. Generally, the animals show locomotory
movements in search of food, mate and shelter. It also helps the animals
to run from the adverse environmental conditions, and to move away from the
predators.
Movements of limbs, appendages, head and trunk serve to change the posture of the body and maintain equilibrium against the gravity. For example, taking in of food involves the movements of tongue, jaws, snout, limbs in man; movements of external ear and eyeballs help to perceive the informations from the outside environments; movements of alimentary canal help to pass the food down; movements of heart circulate the blood in the body; lungs are ventilated by the movements of thoracic muscles and diaphragm etc.
Besides such locomotion and movements of the body, multicellular organisms can also move their individual cells like the movements seen in unicellular organisms. Some of the white blood cells and macrophages, which are phagocytic in nature, move through the tissues by amoeboid movements to reach the places of infection. Ciliary movements occur in the upper respiratory tract, fallopian tubes and vasa efferentia tubes of testes. A mammalian sperm moves into the female reproductive tract by the flagellar movements. In sponges, flagellar movements of some cells occur to maintain the water current in them.
Most of the multicellular animals have muscle fibres for locomotion, limb movements as well as movements of internal organs. In all higher animals (vertebrates) there are mainly two systems that bring about movement and locomotion of the body. These two systems are skeletal system and muscular system that work in coordination with each other. The force generated by muscle contraction is utilised to move bones of the skeleton like levers. This results in movements of limbs and appendages. So the muscles working with the skeletal system are called skeletal muscles.
Movements of limbs, appendages, head and trunk serve to change the posture of the body and maintain equilibrium against the gravity. For example, taking in of food involves the movements of tongue, jaws, snout, limbs in man; movements of external ear and eyeballs help to perceive the informations from the outside environments; movements of alimentary canal help to pass the food down; movements of heart circulate the blood in the body; lungs are ventilated by the movements of thoracic muscles and diaphragm etc.
Besides such locomotion and movements of the body, multicellular organisms can also move their individual cells like the movements seen in unicellular organisms. Some of the white blood cells and macrophages, which are phagocytic in nature, move through the tissues by amoeboid movements to reach the places of infection. Ciliary movements occur in the upper respiratory tract, fallopian tubes and vasa efferentia tubes of testes. A mammalian sperm moves into the female reproductive tract by the flagellar movements. In sponges, flagellar movements of some cells occur to maintain the water current in them.
Most of the multicellular animals have muscle fibres for locomotion, limb movements as well as movements of internal organs. In all higher animals (vertebrates) there are mainly two systems that bring about movement and locomotion of the body. These two systems are skeletal system and muscular system that work in coordination with each other. The force generated by muscle contraction is utilised to move bones of the skeleton like levers. This results in movements of limbs and appendages. So the muscles working with the skeletal system are called skeletal muscles.
Movements
in some invertebrates:
There are also many invertebrates like jellyfish, earthworm and leech, which are devoid of skeletons but possess muscles for their movements.
Movements in Hydra:
Hydra lacks a well-developed muscular system. They have two types of contractile cells on its body wall, viz. epitheliomuscular cells in the outer layer of the body wall and the nutritive muscular cells in the inner layer. Contractions and relaxations of these cells, respectively, shorten and elongate their processes. Various types of movements seen in Hydra are looping, somersaulting, climbing, shortening and elongation etc.
Movements in Annelids:
Earthworms and leeches have muscle fibres of the body wall that help these animals to crawl on land. These muscle fibres are of two types – longitudinal muscle fibres; and circular muscle fibres. In earthworms, the locomotion of the body is brought about by alternate contraction of circular and longitudinal muscles, causing waves of thinning and thickening to pass backwards. It involves partly a pushing of the anterior end and partly of the posterior end. The coelomic fluid gives turgidity as it acts as a hydraulic skeleton making the body wall tough. The worm moves at the rate of about 25 cm per minute.
Movements in Starfish:
Starfishes have got a water vascular system that help them in their locomotion. Each arm of the starfish has two rows of tube feet underneath. Water enters into these tube feet by the muscular contractions and this moves the animal over the surface of the substratum in water. Starfishes are bottom dwellers found in sea waters only.
Movements in higher vertebrates:
In higher animals, movements and locomotion depend on the association of skeletal muscles with the skeletal system.
There are also many invertebrates like jellyfish, earthworm and leech, which are devoid of skeletons but possess muscles for their movements.
Movements in Hydra:
Hydra lacks a well-developed muscular system. They have two types of contractile cells on its body wall, viz. epitheliomuscular cells in the outer layer of the body wall and the nutritive muscular cells in the inner layer. Contractions and relaxations of these cells, respectively, shorten and elongate their processes. Various types of movements seen in Hydra are looping, somersaulting, climbing, shortening and elongation etc.
Movements in Annelids:
Earthworms and leeches have muscle fibres of the body wall that help these animals to crawl on land. These muscle fibres are of two types – longitudinal muscle fibres; and circular muscle fibres. In earthworms, the locomotion of the body is brought about by alternate contraction of circular and longitudinal muscles, causing waves of thinning and thickening to pass backwards. It involves partly a pushing of the anterior end and partly of the posterior end. The coelomic fluid gives turgidity as it acts as a hydraulic skeleton making the body wall tough. The worm moves at the rate of about 25 cm per minute.
Movements in Starfish:
Starfishes have got a water vascular system that help them in their locomotion. Each arm of the starfish has two rows of tube feet underneath. Water enters into these tube feet by the muscular contractions and this moves the animal over the surface of the substratum in water. Starfishes are bottom dwellers found in sea waters only.
Movements in higher vertebrates:
In higher animals, movements and locomotion depend on the association of skeletal muscles with the skeletal system.
Movement in Human Beings:
3 types of movement are observed:
1.
Amoeboid Movemnt: Macrophages and
leucoycytes of blood show amoeboid movement. It takes place by finger like
projections or pseudopodia formed by cytoplasmic streaming. Cytoskeletal
elements like microfilamenst are also involved.
2.
Ciliary movement: Cilia are small
hair like structures arising from cytoplasmic basal granules. In humans,
internal and tubular organs are lined by ciliated epithelium. Cilia in these
organs beat in coordination.
The coordinated movement of cilia in
trachea helps in removing dust particles and some of the foreign substances
inhaled along with atmospheric air.
Passage of ova through female
reproductive tract is also facilitated by ciliary movement.
3.
Muscular movement: Brought about by
action of specific types of muscles. It is involved in the movement of limbs,
jaws, tongue etc.
Muscular movement is based on
contractile property of muscles.
Locomotion in human beings and most
multicellular animals requires a perfect coordinated activity of muscular,
skeletal and neural systems.
Skeletal Muscle:
Structure
Each
skeletal muscle is made of a many muscle bundles or fascicles that are
held together by a common cartilaginous connective tissue layer called as fascia.
Each
muscle bundle is made of a number of muscle fibre.
(figure 20.1)
Muscle bundles (fascicles) →Muscle fibre →Myofibrils
or myofilaments → Actin and Myosin
Muscle Fibre: Each muscle fibre is lined by the plasma membrane
called sarcolemma that encloses the sarcoplasm. The muscle fibre is a syncitium
or multinucleate. The muscle fibre also contains endoplasmic reticulum or
sarcoplasmic reticulum. The sarcoplasmic reticulum of muscle fibre is store house
of calcium ions.
The
sarcoplasm of each muscle fibre is characterized by many parallel arranged
filaments known as myofilamnents or myofibrils.
Myofilaments or Myofibrils: Each myofibril is characterized by striated
appearance or alternate dark and light bands. This striated appearance of
myofibrils is due to specific distribution of two important proteins – Actin
and Myosin. The two proteins are arranged as rod like structures
parallel to each other and to the longitudinal axis of myofibrils.
Light Bands contain actin and are also called I Band or
Isotropic band.
Dark Band contains myosin and is also called A Band or
Anisotropic band.
Actin
filaments are thinner than myosin, hence actin are also called thin filaments
and myosin are called thick filaments.
In the
centre of I band or thin filaments, there is an elastic fibre which bisects it
– Z line. The thin filaments are firmly attached to the z-line.
The thick
filaments are similarly held together in the middle by thin fibrous membrane
called M – line.
The A and
I bands are alternately arranged throughout the myofibrils.
The
portion of myofibril between
two consecutive z lines is known
as a sarcomere. Sarcomere is considered as a functional unit of
muscle contraction.
Figure 20.2
In resting state, the edges of thin
filaments on either side of thick filaments overlap the ends of thick filaments
partially, leaving central part of thick filaments. This central part of thick
filaments, not overlapped by thin filaments is known as H-zone.
Structure of Actin (Thin Filaments) (figure 20.3 a)
Each actin is made of:
·
2 F (filamentous) actins:
The 2 filaments of F actins are helically wound around each
other. Each of these F actins is a polymer of 13 monomeric globular or G actins. Each of these
G-actin molecules have active sites for ADP molecules that act as binding sites
for heads of myosin.
·
2 tropomyosin filaments that run
close to the F filaments and are intercoiled with it.
·
Troponin, a complex oval shaped protein
that is distributed at regular intervals on the tropomyosin.
In resting state, a troponin subunit
covers the active binding site for myosin on actin filament.
Structure
of Myosin (Thick Filaments) (figure 20.3 b)
The thick filaments of myosin is a
polymerized protein, like actin. The monomers forming myosin are Meromyosin. The myosin is formed of 6
polypeptide chains and is differentiated in to 2 parts:
a.
Head: 2 in number and globular with
a short arm. Head formed of HMM or
heavy meromyosin. Together with short arm, head is known as crossarm.
The crossarms project outward at
regular intervals and at an angle from each other from the surface of
polymerized myosin filament. It forms cross bridges with actin filaments in
presence of enzyme myosinATPase which
is present on the heads.
Thus the head is:
§
An active ATPase enzyme
§
Binding site for ATP
§
Active sites for actin
b.
Tail:LMM or light meromyosin.
Mechanism of Muscle Contraction
Explained on the basis of Sliding
Filament Theory proposed by Huxley, Huxley and Hansen (1984).
According to this theory, muscle
fibre contraction takes place by sliding of thin filaments over the thick
filaments.
The following changes occur in the
banding pattern of sarcomeres of striated muscle fibre:
1.
Length of A band remains unchanged
2.
Distance between adjacent H zones
remains constant
4.
Distance between adjacent Z-lines
and the size of sarcomere decreases
On the basis of above changes,
following proposals were mad:
o
Head of myosin filaments come in
close contact with actin filaments to form actomyosin complexes
o
Heads undergo swiveling (rotation),
which pulls actin filaments inward over myosin filaments
This decreases the length of
sarcomere without any change in size of A-bands and H-bands. A similar action
in all sarcomere causes shortening of whole myofibril and thereby of whole
muscle fibre.
Steps
in Muscle Contraction: (figure 20.4)
1)
Muscle contraction is initiated by
signal sent by the CNS (Central Nervous System), through a motor neuron.
The motor neuron and the muscle
fibre together form the motor unit.
The junction between the motor
neuron and the sarcolemma of the muscle fibre is known as neuromuscular
junction or the motor end plate.
When motor nerve impulse reaches the
neuromuscular junction, the synaptic vesicle present in motor end plate secrete
the neurotransmitter chemical acetylcholine.
2)
The acetylcholine binds to receptors
on sarcolemma, causes its depolarization and generates the action potential in sacrolemma.
3)
Action potential stimulates
sarcoplasmic reticulum to release calcium ions that initiate biochemical
changes in muscle contraction.
When 4 calcium ions combine with
troponin C, then it moves the tropomyosin molecule deeper in to the groove between
the two actin strands. This uncovers the active sites of actin molecules to
allow the binding of meromyosin head of myosin.
4)
Myosin ATPase hydrolyses ATP,
releasing energy. The energy stimulates the formation of actomyosin complexes
between head of myosin and active sites on actin. Thus the cross bridge is
formed between actin and myosin.
Due to interlinking, heads get
tilted and this tilt of head is known as power stroke.
5)
The energy releases also causes
rotation or swiveling of heads of myosin filaments which pulls actin filaments
inwards.
6)
Next, heads of myosin separate from
actin, and then swing back to their original position. Another ATP is
hydrolysed, more energy is released and rotation of myosin head is repeated.
Thus actin filaments further slide inward towards the A band. The Z line
attached to these bands also gets pulled inward. This causes shortening of
myofibril called contraction.
Thus
during contraction:
o
I band retains its length
o
A bands retains its length
7)
The myosin releases the ADP and Pi
and goes back to its original relaxed state. A new ATP binds and the cross
bridge is broken.
8)
After maximum muscle contraction, Ca2+
from sarcoplasm is trapped by sarcoplasmic reticulum. The actin filaments are
masked again. This inactivates myosin ATPase enzyme, so energy is no more
available. The actomyosin complex
dissociates and actin filaments get back to original position of muscle
relaxation.
9)
During muscle relaxation
repolarization occurs.
Muscle
Fatigue:
Repeated activation of muscles can
lead to accumulation of lactic acid due to anaerobic breakdown of glycogen in
them. This is known as Muscle fatigue.
Factors causing muscle fatigue:
o
Accumulation of lactic acid
o
Heavy exercise: snce lactic acid
formation is faster than its oxidation. And the muscle fibres undergo oxygen
debt.
o
Decreased ATP supply to muscle
fibres.
o
Decreased blood supply to muscle
fibres.
Movements
of Skeletal Muscles:
The skeletal muscles are made of striated muscle fibres and are under voluntary control. According to the type of movements, skeletal muscles can be classified as under:
1. Flexor. A muscle that bends one part upon another (e.g., leg upon thigh)
2. Extensor. The muscles responsible for straightening out a part of the body are termed extensor muscles (e.g., muscles concerned with the extension of foot).
3. Adductor. The muscle that is concerned with the movement of a part of the body towards the midline of the body is called the adductor muscle.
4. Abductor. The muscle which moves a part of the body away from the midline of the body is termed as abductor muscle.
5. Pronator. A muscle that brings about the rotation of body parts. For example, the rotation of fore arm to turn the palm downward or backward.
6. Supinator. It helps to rotate the fore arm and thus make the palm face upward or forward.
Antagonistic muscles:
When the two muscles contract to bring out opposite movements at the same place, then they are called as antagonistic muscles. For example, biceps muscles present in the arm is a flexor for the elbow joint; and the triceps is its antagonistic muscle and acts as an extensor for that joints. During flexion movements the biceps contracts and triceps relaxes; while during extension movements biceps relaxes and triceps contracts.
The skeletal muscles are made of striated muscle fibres and are under voluntary control. According to the type of movements, skeletal muscles can be classified as under:
1. Flexor. A muscle that bends one part upon another (e.g., leg upon thigh)
2. Extensor. The muscles responsible for straightening out a part of the body are termed extensor muscles (e.g., muscles concerned with the extension of foot).
3. Adductor. The muscle that is concerned with the movement of a part of the body towards the midline of the body is called the adductor muscle.
4. Abductor. The muscle which moves a part of the body away from the midline of the body is termed as abductor muscle.
5. Pronator. A muscle that brings about the rotation of body parts. For example, the rotation of fore arm to turn the palm downward or backward.
6. Supinator. It helps to rotate the fore arm and thus make the palm face upward or forward.
Antagonistic muscles:
When the two muscles contract to bring out opposite movements at the same place, then they are called as antagonistic muscles. For example, biceps muscles present in the arm is a flexor for the elbow joint; and the triceps is its antagonistic muscle and acts as an extensor for that joints. During flexion movements the biceps contracts and triceps relaxes; while during extension movements biceps relaxes and triceps contracts.
Red and White Muscle Fibres:
Muscle
contains a red coloured oxygen storing pigment called myoglobin. Some muscles
have a higher myoglobin content giving it a red coloured appearance, these are
known as Red Fibres. In contrast muscles with lower myoglobin content are known
as White muscle Fibres.
|
Characters
|
Red
(Aerobic) Muscle fibres
|
White
(Anaerobic) Muscle Fibres
|
|
Size
|
Smaller
and thinner
|
Longer
and thicker
|
|
Innervation
|
Innervated
by small nerve fibre
|
Innervated
by longer nerve fibre
|
|
Blood
Supply
|
High
|
Low
|
|
Mitochondria
|
More
in number as depend on energy provided by aerobic cell respiration
|
Less
in number as depend on energy provided by glycolytic pathway
|
|
Colour
|
Dark
red due to myoglobin which stores oxygen
|
Light
coloured as no myoglobin
|
|
Sarcoplasmic
reticulum
|
Less
developed
|
More
developed
|
|
Mode
of contraction
|
Slow
but sustained
|
Rapid
but of Short duration
|
|
Fatigue
|
Do
not undergo fatigue
|
Undergo
early fatigue
|
|
Examples
|
Extensor
muscles of back, flight muscles in kites, pigeons etc
|
Eye
ball muscles, and flight muscles of sparrow
|
Skeletal System
The skeletal system consists
of a network of specialised rigid connective tissue called bones and
elastic cartilage.
Bones vs cartilage
o
Bone is hard with a very hard matrix
due to calcium salts in it
o
Cartilage is slightly elastic due to
chondroitin salts.
This skeletal system consists of many parts,
each made of one or more bones. According to the shape and size, bones
may be long (thigh bone and the upper arm bone); flat (breast bone and the
shoulder girdle bone); or irregular (bones of the vertebral column).
The human skeletal system consists
of 206 bones and some cartilages. Human babies have 306 bones.
The human skeletal system is divided
in to 2 main parts:
Axial
skeletal system
Appendicular
skeletal system
AXIAL
SKELETAL SYSTEM
It lies along the longitudinal axis
of the body and includes 80 bones:
Ø
Skull: 29 bones including
ü
Cranium = 8 bones
ü
Face = 14 bones
ü
Ear ossicles= 6
ü
Hyoid=1
Ø
Vertebrae=26 (33 in children)
Ø
Sternum=1
Ø
Ribs=24
I.
SKULL:
Skull is endoskeleton of head, and lies at the upper end of vertebral column.
It is the heaviest part of the body and consists of 4 parts; cranium, face,
hyoid, and sensory capsules.
Cranium
or brain box: large and hollow part that
encloses and protects the brain. The cranial aperture Foramen Magnum, is the site where brain and spinal cord are
connected.
Human
skull is Dicondylic, i.e. with two
occipital condyles on the two sides of foramen magnum.
Cranium
is formed of 8 bones:
|
Frontal
|
1
|
Temporal
|
2
|
|
Parietal
|
2
|
Sphenoid
|
1
|
|
Occipital
|
1
|
Ethmoid
|
1
|
Temporals
also have middle ear bones: incus, malleus and stapes (smallest
bone of body).
Facial
Region: Formed of 14 bones
|
Nasals
|
2
|
Inferior
turbinals
|
2
|
|
Vomer
|
1
|
Lacrymals
|
2
|
|
Zygomatics
(molars)
|
2
|
Palatines
|
2
|
|
Maxillae
|
2
|
Mandibles
|
1
|
Hyoid:
Horse shoe shaped bone which supports throat and provides surface for
attachment of tongue muscles.
II.
VERTEBRAL
COLUM OR SPINAL COLUMN: Also known as backbone. 70 cm long
and present on dorsal side of neck and trunk. It extends from base of skull and
constitutes the main framework of the trunk.
Vertebral column of man is formed of
26 ring like vertebrae. All the vertebrae are amphiplatyan type, i.e. with centrum flat on both sides.
Vertebral
formula of man: C7Th12L5S(5)Co(4)
|
Name of vertebrae
|
Region
|
Number
|
|
Cervical
|
Neck
|
7
|
|
Thoracic
|
Chest
or Thorax
|
12
|
|
Lumbar
|
Upper
abdomen
|
5
|
|
Sacrum
|
Upper
Pelvis
|
1
(formed by fusion of 5 sacral vertebra)
|
|
Coccygeal
(Tail Bone)
|
Lower
Pelvis
|
1
(Formed by fusion of 4 coccygeal vertebra)
|
Each
vertebra has a central hollow portion (neural canal) through which the spinal
cord passes.
First
vertebra (cervical) is the Atlas. It
has no centrum and neural spine. It
articulates with the occipital condyles.
The
number of cervical vertebra is 7 in almost all mammals including humans.
Functions
of Vertebral Column:
1.
Atlas vertebra supports the head and
its ‘yes’ movement.
2.
Axis vertebra support the rotator
and sideways (no) movement of head.
3.
Lumbar vertebrae help in erect
posture and bipedal locomotion
4.
Neural canal of vertebral column encloses
and protects the spinal cord.
5.
Thoracic vertebrae provides surface
for attachment of ribs
6.
Sacrum has facets for attachment of
ilia of pelvic girdles.
III.
RIBS:
12 pairs. Each rib is formed of 2 parts:
·
posterior bony vertebral part
·
anterior cartilaginous sterna part
On
the basis of sterna parts, ribs are of 3 types:
i.
True or Vertebrosternal ribs: first
7 pairs. Sterna parts are directly attached to sternum through costal
cartilages.
ii.
False ribs: 3 pairs. Sternal parts
are attached to the 7th pair of ribs and not to the sternum
directly.
iii.
Floating ribs: 2 pairs. Sterna parts
remain free.
Each rib has two articulation
surfaces
Functions
of ribs:
1.
Thoracic vertebra, sternum and ribs
together from a bony thoracic basket to protect lungs and heart.
2.
Ribs also play an important part in
respiration.
3.
Floating ribs protect the kidney.
IV.
STERNUM:
(Breast Bone). Flat elongated dagger shaped bone present on
midventral side of thorax.
APPENDICULAR SKELETAL SYSTEM (126 Bones)
Comprises of:
·
Bones of limb
·
Girdles
I.
LIMBS:
There are 2 pairs of limbs: Forelimb and Hind limb. Each limb is made of 30
bones.
I.
Forelimbs: The bones
of forelimb or hands comprise of:
Figure 20.9
|
Region
|
Bones
|
Number
|
|
Upper
Arm
|
Humerus
|
1
|
|
Forearm
|
Radius
|
1
|
|
Ulna
|
1
|
|
|
Wrist
|
Carpals
|
8
|
|
Palm
|
Metacarpals
|
5
|
|
Fingers
|
Phalanges
|
14
|
II.
Hindlimbs:
Hindlimb or leg bones are longer than those of forelimbs. They comprise of:
Figure 20.10
|
Region
|
Bones
|
Number
|
|
Thigh
|
Femur
|
1
|
|
Shank
|
Tibia
|
1
|
|
Fibula
|
1
|
|
|
Ankle
|
Tarsals
|
7
|
|
Instep
|
Metatarsals
|
5
|
|
Toes
|
Phalanges
|
14
|
|
Knee
Joint
|
Patella
|
1
|
III.
Girdles:
The pectoral and pelvic girdles help in articulation of upper and lower limbs
respectively, with the axial skeleton.
A.
Pectoral Girdle:
Formed of 2 halves. It comprises of:
1.
Clavicle or collar bone: Rod like
S-shaped bone. It is long and slender with two curvatures. Connects sternum and
acromion of Scapula.
2.
Scapula: large triangular flat bone
situated in dorsal part of thorax, between second and seventh ribs.
It
has a slightly elevated ridge like spine that projects as a flat expanded
process called acromion.
Below
acromion is a depression called glenoid
cavity. It articulates with head of humerus to form the shoulder joint.
Functions:
Provides articulation to arm bones
B.
Pelvic Girdle:
Present in lower part of trunk. Consists of 2 coaxal bones.
Each coxal bone is formed of fusion of three bones: Ilium, Ischium, and Pubis.
Each coxal bone is formed of fusion of three bones: Ilium, Ischium, and Pubis.
At
the point of fusion of these 3 bones is a cavity called acetabulum. The thigh
bone (femur) articulates with the acetabulum.
The
two halves of pelvic bone meet ventrally to form pubic symphysis containing
fibrous cartilage.
Functions:
The two parts of pelvic girdle form a bowl like space called pelvis. The pelvis
supports and protects the abdominal viscera.
It
lowers centre of gravity and helps in erect posture.
The
pelvic girdle of females is more flexible, broader and shallower than those of
males. It is an adaptation for pregnancy and child birth.
Functions of skeletal system:
1. It provides a kind of framework for the body.
2. It provides shape and posture to the body.
3. It provides protection to some of the inner delicate organs like brain, spinal cord and lungs.
4. It gives rigid surface for the attachment of muscles with the help of tendons.
5. It helps in locomotion.
6. The bone marrow serves as the centre for the production of red blood cells and white blood cells.
7. The movements of ribs and sternum help in breathing.
8. In the ear, the sound vibrations are conveyed from the tympanum to the internal ear by a set of three bones as in man.
9. It helps the body to be an integrated unit.
10. It serves to store various ions like calcium and phosphate, which are then released into the body at the time of need. These minerals perform various functions of the body.
Joints:
The junctions where two or more bones articulate with each other are known as joints. These joints allow the movement of bones in different ways. According to the mobility they are of the following types:
1. Fixed or immovable or fibrous joints: At these joints the bones are held firmly together and movements are not allowed in between them. At these joints a dense and tough inextensible white fibrous tissue is present. For example, sutures that join the various bones of the skull.
2. Slightly movable or cartilaginous joints: At these joints a dense disc of white fibrocartilage is present that joins the opposite surfaces of the articulating bones. It allows only a little movement like bending and rotation. These joints are seen in between the vertebrae.
3. Freely movable or synovial joints: In this type of joint there is a fluid filled synovial cavity in between the movably articulated bones. The fluid is called as synovial fluid. A synovial membrane covers this fluid filled synovial cavity forming the capsule. The articulating bones are provided with cartilage caps. Ligaments are also present to hold the bones. It is of the following types:
(i) Ball and socket joint. In this, one of the bones forms a globular head while the other forms a cup – like socket into which head fits in. It allows a free movement in all directions e.g., shoulder girdle and hip girdle joints. Such joints may stretch (extend), fold (flex) and rotate the limb of the body. This may allow the movement of the limb towards the body or away from the body.
(ii) Hinge joint. Here the two bones are fitted like the hinge of a door so as to allow to and fro movements in one direction only. These joints are provided with strong ligaments. It is seen in elbow joint, knee joint and joints between phalanges of fingers and toes.
(iii) Pivot joint. In this type of joint, one bone is fixed while the other moves freely over it. The movement is, therefore, confined to a rotation around a longitudinal axis through the centre of the pivot e.g., movement of the skull over the odontoid processes of the first neck vertebra.
(iv)Gliding joint It is a biaxial joint, the articulating bones of which can glide one above the other. It is seen in wrist bones that can glide over forearm bones, in zygapophysis by which vertebrae can glide one above the other e.g., some of the bones in the palm or in the sole of foot.
(v)Ellipsoid joints. They permit movements of articulating bones around two axes. Such joints are formed between the toe bones and some bones in the sole of foot.
Movements are produced at joints by contractions of skeletal muscles inserted into the articulating bones. Flexible connective tissue bonds called ligaments stabilise the joints by holding the articulating bones together.
